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><A
NAME="SPI-EXAMPLES"
>43.5. Examples</A
></H1
><P
>   This section contains a very simple example of SPI usage. The
   procedure <CODE
CLASS="FUNCTION"
>execq</CODE
> takes an SQL command as its
   first argument and a row count as its second, executes the command
   using <CODE
CLASS="FUNCTION"
>SPI_exec</CODE
> and returns the number of rows
   that were processed by the command.  You can find more complex
   examples for SPI in the source tree in
   <TT
CLASS="FILENAME"
>src/test/regress/regress.c</TT
> and in the
   <A
HREF="contrib-spi.html"
>spi</A
> module.
  </P
><PRE
CLASS="PROGRAMLISTING"
>#include "postgres.h"

#include "executor/spi.h"
#include "utils/builtins.h"

#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif

int execq(text *sql, int cnt);

int
execq(text *sql, int cnt)
{
    char *command;
    int ret;
    int proc;

    /* Convert given text object to a C string */
    command = text_to_cstring(sql);

    SPI_connect();

    ret = SPI_exec(command, cnt);

    proc = SPI_processed;
    /*
     * If some rows were fetched, print them via elog(INFO).
     */
    if (ret &gt; 0 &amp;&amp; SPI_tuptable != NULL)
    {
        TupleDesc tupdesc = SPI_tuptable-&gt;tupdesc;
        SPITupleTable *tuptable = SPI_tuptable;
        char buf[8192];
        int i, j;

        for (j = 0; j &lt; proc; j++)
        {
            HeapTuple tuple = tuptable-&gt;vals[j];

            for (i = 1, buf[0] = 0; i &lt;= tupdesc-&gt;natts; i++)
                snprintf(buf + strlen (buf), sizeof(buf) - strlen(buf), " %s%s",
                        SPI_getvalue(tuple, tupdesc, i),
                        (i == tupdesc-&gt;natts) ? " " : " |");
            elog(INFO, "EXECQ: %s", buf);
        }
    }

    SPI_finish();
    pfree(command);

    return (proc);
}</PRE
><P
>   (This function uses call convention version 0, to make the example
   easier to understand.  In real applications you should use the new
   version 1 interface.)
  </P
><P
>   This is how you declare the function after having compiled it into
   a shared library (details are in <A
HREF="xfunc-c.html#DFUNC"
>Section 35.9.6</A
>.):

</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FUNCTION execq(text, integer) RETURNS integer
    AS '<TT
CLASS="REPLACEABLE"
><I
>filename</I
></TT
>'
    LANGUAGE C;</PRE
><P>
  </P
><P
>   Here is a sample session:

</P><PRE
CLASS="PROGRAMLISTING"
>=&gt; SELECT execq('CREATE TABLE a (x integer)', 0);
 execq
-------
     0
(1 row)

=&gt; INSERT INTO a VALUES (execq('INSERT INTO a VALUES (0)', 0));
INSERT 0 1
=&gt; SELECT execq('SELECT * FROM a', 0);
INFO:  EXECQ:  0    -- inserted by execq
INFO:  EXECQ:  1    -- returned by execq and inserted by upper INSERT

 execq
-------
     2
(1 row)

=&gt; SELECT execq('INSERT INTO a SELECT x + 2 FROM a', 1);
 execq
-------
     1
(1 row)

=&gt; SELECT execq('SELECT * FROM a', 10);
INFO:  EXECQ:  0
INFO:  EXECQ:  1
INFO:  EXECQ:  2    -- 0 + 2, only one row inserted - as specified

 execq
-------
     3              -- 10 is the max value only, 3 is the real number of rows
(1 row)

=&gt; DELETE FROM a;
DELETE 3
=&gt; INSERT INTO a VALUES (execq('SELECT * FROM a', 0) + 1);
INSERT 0 1
=&gt; SELECT * FROM a;
 x
---
 1                  -- no rows in a (0) + 1
(1 row)

=&gt; INSERT INTO a VALUES (execq('SELECT * FROM a', 0) + 1);
INFO:  EXECQ:  1
INSERT 0 1
=&gt; SELECT * FROM a;
 x
---
 1
 2                  -- there was one row in a + 1
(2 rows)

-- This demonstrates the data changes visibility rule:

=&gt; INSERT INTO a SELECT execq('SELECT * FROM a', 0) * x FROM a;
INFO:  EXECQ:  1
INFO:  EXECQ:  2
INFO:  EXECQ:  1
INFO:  EXECQ:  2
INFO:  EXECQ:  2
INSERT 0 2
=&gt; SELECT * FROM a;
 x
---
 1
 2
 2                  -- 2 rows * 1 (x in first row)
 6                  -- 3 rows (2 + 1 just inserted) * 2 (x in second row)
(4 rows)               ^^^^^^
                       rows visible to execq() in different invocations</PRE
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